The performance of an internal combustion engine can be improved by the use of dual camshafts, one to operate the intake valves of the various cylinders of the engine and the other to operate the exhaust valves. Typically, one of such camshafts is driven by the crankshaft of the engine, through a sprocket and chain drive or a belt drive, and the other of such camshafts is driven by the first, through a second sprocket and chain drive or a second belt drive. Alternatively, both of the camshafts can be driven by a single crankshaft powered chain drive or belt drive. A crankshaft can take power from the pistons to drive at least one transmission and at least one camshaft. Engine performance in an engine with dual camshafts can be further improved, in terms of idle quality, fuel economy, reduced emissions or increased torque, by changing the positional relationship of one of the camshafts, usually the camshaft which operates the intake valves of the engine, relative to the other camshaft and relative to the crankshaft, to thereby vary the timing of the engine in terms of the operation of intake valves relative to its exhaust valves or in terms of the operation of its valves relative to the position of the crankshaft.
As is conventional in the art, there can be one or more camshafts per engine. A camshaft can be driven by a belt, or a chain, or one or more gears, or another camshaft. One or more lobes can exist on a camshaft to push on one or more valves. A multiple camshaft engine typically has one camshaft for exhaust valves, one camshaft for intake valves. A “V” type engine usually has two camshafts (one for each bank) or four camshafts (intake and exhaust for each bank).
Variable cam timing (VCT) devices are generally known in the art, such as U.S. Pat. No. 7,841,311; U.S. Pat. No. 7,789,054; U.S. Pat. No. 7,270,096; U.S. Pat. No. 6,725,817; U.S. Pat. No. 6,244,230; and U.S. Published Application No. 2010/0050967. Known patents and publications disclose hydraulic couplings for phaser assemblies in which an annular space is provided between a drive stator member concentrically surrounding one or more driven rotor members. An annular space between the members can be divided into segment-shaped or arcuate variable volume working chambers by one or more vanes extending radially inward from an inner surface of the drive stator member and one or more vanes extending radially outward from an outer surface of the one or more driven rotor members. As hydraulic fluid is admitted into and expelled from the various chambers, the vanes rotate relative to one another and thereby vary the relative angular position of the drive stator member and the one or more driven rotor members. Hydraulic couplings that use radial vanes to apply a tangentially acting force will be referred to herein as vane-type hydraulic couplings. Each of these prior known patents and publications appears to be suitable for its intended purpose. However, it would be desirable to provide a variable cam timing phaser with a simplified fluid flow passage configuration. It would be desirable to provide a variable cam timing phaser having common shared fluid passage portions. It would be desirable to provide a variable cam timing phaser having a shared control valve for one or more phase shifting driven rotors.